A system is conventionally known that enables multiple terminals to share information such as a desktop screen. For example, in the case of causing a terminal to display PC screen information, a technique is known which does not display the entire PC screen on the terminal but trims the image in a size of the screen of the terminal and displays the trimmed image on the terminal (for example, see Japanese Laid-open Patent Publication No. 2004-005582). Related techniques are also disclosed in, for example, Japanese Laid-open Patent Publication No. 05-206959.
However, the conventional technique has a problem that unnecessary communications take place in the case of a change in information shared by the terminals because the change is so slight that one of the terminals is not capable of expressing the change.
In view of the above, an aspect aims to provide a technique which enables efficient data transmission.